go/proxyd: Add integration tests and batch support

.github/workflows/proxyd.yml

+name: proxyd unit tests
+
+on:
+  push:
+    branches:
+      - 'master'
+      - 'develop'
+  pull_request:
+  workflow_dispatch:
+
+defaults:
+  run:
+    working-directory: ./go/proxyd
+
+jobs:
+  test:
+    steps:
+    - name: Install Go
+      uses: actions/setup-go@v2
+      with:
+        go-version: 1.15.x
+
+    - name: Checkout code
+      uses: actions/checkout@v2
+
+    - name: Build
+      run: make proxyd
+
+    - name: Lint
+      run: make lint
+
+    - name: Test
+      run: make test

go/proxyd/Makefile

@@ -11,3 +11,11 @@ fmt:
 	go mod tidy
 	gofmt -w .
 .PHONY: fmt
+
+test:
+	go test -race -v ./...
+.PHONY: test
+
+lint:
+	go vet ./...
+.PHONY: test
\ No newline at end of file

go/proxyd/backend.go

@@ -62,6 +62,10 @@ var (
 		Message:       "backend returned an invalid response",
 		HTTPErrorCode: 500,
 	}
+	ErrTooManyBatchRequests = &RPCErr{
+		Code:    JSONRPCErrorInternal - 14,
+		Message: "too many RPC calls in batch request",
+	}
 )
 
 func ErrInvalidRequest(msg string) *RPCErr {
@@ -631,7 +635,7 @@ func (w *WSProxier) close() {
 }
 
 func (w *WSProxier) prepareClientMsg(msg []byte) (*RPCReq, error) {
-	req, err := ParseRPCReq(bytes.NewReader(msg))
+	req, err := ParseRPCReq(msg)
 	if err != nil {
 		return nil, err
 	}

go/proxyd/cache.go

@@ -62,6 +62,7 @@ func (c *redisCache) Get(ctx context.Context, key string) (string, error) {
 	if err == redis.Nil {
 		return "", nil
 	} else if err != nil {
+		RecordRedisError("CacheGet")
 		return "", err
 	}
 	return val, nil
@@ -69,6 +70,9 @@ func (c *redisCache) Get(ctx context.Context, key string) (string, error) {
 
 func (c *redisCache) Put(ctx context.Context, key string, value string) error {
 	err := c.rdb.Set(ctx, key, value, 0).Err()
+	if err != nil {
+		RecordRedisError("CacheSet")
+	}
 	return err
 }
 
@@ -105,6 +109,7 @@ func (c *rpcCache) GetRPC(ctx context.Context, req *RPCReq) (*RPCRes, error) {
 		return nil, err
 	}
 	if !cacheable {
+		RecordCacheMiss(req.Method)
 		return nil, nil
 	}
 
@@ -114,6 +119,7 @@ func (c *rpcCache) GetRPC(ctx context.Context, req *RPCReq) (*RPCRes, error) {
 		return nil, err
 	}
 	if encodedVal == "" {
+		RecordCacheMiss(req.Method)
 		return nil, nil
 	}
 	val, err := snappy.Decode(nil, []byte(encodedVal))
@@ -121,6 +127,7 @@ func (c *rpcCache) GetRPC(ctx context.Context, req *RPCReq) (*RPCRes, error) {
 		return nil, err
 	}
 
+	RecordCacheHit(req.Method)
 	res := new(RPCRes)
 	err = json.Unmarshal(val, res)
 	if err != nil {

go/proxyd/cmd/proxyd/main.go

@@ -2,6 +2,8 @@ package main
 
 import (
 	"os"
+	"os/signal"
+	"syscall"
 
 	"github.com/BurntSushi/toml"
 	"github.com/ethereum-optimism/optimism/go/proxyd"
@@ -35,7 +37,14 @@ func main() {
 		log.Crit("error reading config file", "err", err)
 	}
 
-	if err := proxyd.Start(config); err != nil {
+	shutdown, err := proxyd.Start(config)
+	if err != nil {
 		log.Crit("error starting proxyd", "err", err)
 	}
+
+	sig := make(chan os.Signal, 1)
+	signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
+	recvSig := <-sig
+	log.Info("caught signal, shutting down", "signal", recvSig)
+	shutdown()
 }

go/proxyd/config.go

@@ -61,11 +61,11 @@ type MethodMappingsConfig map[string]string
 
 type Config struct {
 	WSBackendGroup    string              `toml:"ws_backend_group"`
-	Server            *ServerConfig       `toml:"server"`
-	Cache             *CacheConfig        `toml:"cache"`
-	Redis             *RedisConfig        `toml:"redis"`
-	Metrics           *MetricsConfig      `toml:"metrics"`
-	BackendOptions    *BackendOptions     `toml:"backend"`
+	Server            ServerConfig        `toml:"server"`
+	Cache             CacheConfig         `toml:"cache"`
+	Redis             RedisConfig         `toml:"redis"`
+	Metrics           MetricsConfig       `toml:"metrics"`
+	BackendOptions    BackendOptions      `toml:"backend"`
 	Backends          BackendsConfig      `toml:"backends"`
 	Authentication    map[string]string   `toml:"authentication"`
 	BackendGroups     BackendGroupsConfig `toml:"backend_groups"`

go/proxyd/go.mod

@@ -4,13 +4,18 @@ go 1.16
 
 require (
 	github.com/BurntSushi/toml v0.4.1
+	github.com/alicebob/gopher-json v0.0.0-20200520072559-a9ecdc9d1d3a // indirect
+	github.com/alicebob/miniredis v2.5.0+incompatible
 	github.com/ethereum/go-ethereum v1.10.11
 	github.com/go-redis/redis/v8 v8.11.4
 	github.com/golang/snappy v0.0.4
+	github.com/gomodule/redigo v1.8.8 // indirect
 	github.com/gorilla/mux v1.8.0
 	github.com/gorilla/websocket v1.4.2
 	github.com/hashicorp/golang-lru v0.5.5-0.20210104140557-80c98217689d
 	github.com/prometheus/client_golang v1.11.0
 	github.com/rs/cors v1.8.0
 	github.com/stretchr/testify v1.7.0
+	github.com/yuin/gopher-lua v0.0.0-20210529063254-f4c35e4016d9 // indirect
+	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
 )

go/proxyd/go.sum

@@ -48,6 +48,10 @@ github.com/alecthomas/template v0.0.0-20190718012654-fb15b899a751/go.mod h1:LOuy
 github.com/alecthomas/units v0.0.0-20151022065526-2efee857e7cf/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=
 github.com/alecthomas/units v0.0.0-20190717042225-c3de453c63f4/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=
 github.com/alecthomas/units v0.0.0-20190924025748-f65c72e2690d/go.mod h1:rBZYJk541a8SKzHPHnH3zbiI+7dagKZ0cgpgrD7Fyho=
+github.com/alicebob/gopher-json v0.0.0-20200520072559-a9ecdc9d1d3a h1:HbKu58rmZpUGpz5+4FfNmIU+FmZg2P3Xaj2v2bfNWmk=
+github.com/alicebob/gopher-json v0.0.0-20200520072559-a9ecdc9d1d3a/go.mod h1:SGnFV6hVsYE877CKEZ6tDNTjaSXYUk6QqoIK6PrAtcc=
+github.com/alicebob/miniredis v2.5.0+incompatible h1:yBHoLpsyjupjz3NL3MhKMVkR41j82Yjf3KFv7ApYzUI=
+github.com/alicebob/miniredis v2.5.0+incompatible/go.mod h1:8HZjEj4yU0dwhYHky+DxYx+6BMjkBbe5ONFIF1MXffk=
 github.com/allegro/bigcache v1.2.1-0.20190218064605-e24eb225f156/go.mod h1:Cb/ax3seSYIx7SuZdm2G2xzfwmv3TPSk2ucNfQESPXM=
 github.com/andreyvit/diff v0.0.0-20170406064948-c7f18ee00883/go.mod h1:rCTlJbsFo29Kk6CurOXKm700vrz8f0KW0JNfpkRJY/8=
 github.com/apache/arrow/go/arrow v0.0.0-20191024131854-af6fa24be0db/go.mod h1:VTxUBvSJ3s3eHAg65PNgrsn5BtqCRPdmyXh6rAfdxN0=
@@ -185,6 +189,8 @@ github.com/golang/snappy v0.0.3/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEW
 github.com/golang/snappy v0.0.4 h1:yAGX7huGHXlcLOEtBnF4w7FQwA26wojNCwOYAEhLjQM=
 github.com/golang/snappy v0.0.4/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEWrmP2Q=
 github.com/golangci/lint-1 v0.0.0-20181222135242-d2cdd8c08219/go.mod h1:/X8TswGSh1pIozq4ZwCfxS0WA5JGXguxk94ar/4c87Y=
+github.com/gomodule/redigo v1.8.8 h1:f6cXq6RRfiyrOJEV7p3JhLDlmawGBVBBP1MggY8Mo4E=
+github.com/gomodule/redigo v1.8.8/go.mod h1:7ArFNvsTjH8GMMzB4uy1snslv2BwmginuMs06a1uzZE=
 github.com/google/btree v0.0.0-20180813153112-4030bb1f1f0c/go.mod h1:lNA+9X1NB3Zf8V7Ke586lFgjr2dZNuvo3lPJSGZ5JPQ=
 github.com/google/btree v1.0.0/go.mod h1:lNA+9X1NB3Zf8V7Ke586lFgjr2dZNuvo3lPJSGZ5JPQ=
 github.com/google/flatbuffers v1.11.0/go.mod h1:1AeVuKshWv4vARoZatz6mlQ0JxURH0Kv5+zNeJKJCa8=
@@ -427,6 +433,8 @@ github.com/valyala/fasttemplate v1.2.1/go.mod h1:KHLXt3tVN2HBp8eijSv/kGJopbvo7S+
 github.com/willf/bitset v1.1.3/go.mod h1:RjeCKbqT1RxIR/KWY6phxZiaY1IyutSBfGjNPySAYV4=
 github.com/xlab/treeprint v0.0.0-20180616005107-d6fb6747feb6/go.mod h1:ce1O1j6UtZfjr22oyGxGLbauSBp2YVXpARAosm7dHBg=
 github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
+github.com/yuin/gopher-lua v0.0.0-20210529063254-f4c35e4016d9 h1:k/gmLsJDWwWqbLCur2yWnJzwQEKRcAHXo6seXGuSwWw=
+github.com/yuin/gopher-lua v0.0.0-20210529063254-f4c35e4016d9/go.mod h1:E1AXubJBdNmFERAOucpDIxNzeGfLzg0mYh+UfMWdChA=
 go.opencensus.io v0.21.0/go.mod h1:mSImk1erAIZhrmZN+AvHh14ztQfjbGwt4TtuofqLduU=
 go.opencensus.io v0.22.0/go.mod h1:+kGneAE2xo2IficOXnaByMWTGM9T73dGwxeWcUqIpI8=
 go.opencensus.io v0.22.2/go.mod h1:yxeiOL68Rb0Xd1ddK5vPZ/oVn4vY4Ynel7k9FzqtOIw=
@@ -520,6 +528,7 @@ golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20180909124046-d0be0721c37e/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20181107165924-66b7b1311ac8/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20181116152217-5ac8a444bdc5/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190204203706-41f3e6584952/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190312061237-fead79001313/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -679,8 +688,9 @@ gopkg.in/yaml.v2 v2.2.8/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.3.0/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.4.0 h1:D8xgwECY7CYvx+Y2n4sBz93Jn9JRvxdiyyo8CTfuKaY=
 gopkg.in/yaml.v2 v2.4.0/go.mod h1:RDklbk79AGWmwhnvt/jBztapEOGDOx6ZbXqjP6csGnQ=
-gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b h1:h8qDotaEPuJATrMmW04NCwg7v22aHH28wwpauUhK9Oo=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gotest.tools v2.2.0+incompatible/go.mod h1:DsYFclhRJ6vuDpmuTbkuFWG+y2sxOXAzmJt81HFBacw=
 honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
 honnef.co/go/tools v0.0.0-20190106161140-3f1c8253044a/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=

go/proxyd/integration_tests/caching_test.go

+package integration_tests
+
+import (
+	"bytes"
+	"fmt"
+	"github.com/alicebob/miniredis"
+	"github.com/ethereum-optimism/optimism/go/proxyd"
+	"github.com/stretchr/testify/require"
+	"os"
+	"testing"
+	"time"
+)
+
+func TestCaching(t *testing.T) {
+	redis, err := miniredis.Run()
+	require.NoError(t, err)
+	defer redis.Close()
+
+	backend := NewMockBackend(RPCResponseHandler(map[string]string{
+		"eth_chainId":          "0x420",
+		"net_version":          "0x1234",
+		"eth_blockNumber":      "0x64",
+		"eth_getBlockByNumber": "dummy_block",
+	}))
+	defer backend.Close()
+
+	require.NoError(t, os.Setenv("GOOD_BACKEND_RPC_URL", backend.URL()))
+	require.NoError(t, os.Setenv("REDIS_URL", fmt.Sprintf("redis://127.0.0.1:%s", redis.Port())))
+	config := ReadConfig("caching")
+	client := NewProxydClient("http://127.0.0.1:8545")
+	shutdown, err := proxyd.Start(config)
+	require.NoError(t, err)
+	defer shutdown()
+
+	// allow time for the block number fetcher to fire
+	time.Sleep(1500 * time.Millisecond)
+
+	tests := []struct {
+		method   string
+		params   []interface{}
+		response string
+	}{
+		{
+			"eth_chainId",
+			nil,
+			"{\"jsonrpc\": \"2.0\", \"result\": \"0x420\", \"id\": 999}",
+		},
+		{
+			"net_version",
+			nil,
+			"{\"jsonrpc\": \"2.0\", \"result\": \"0x1234\", \"id\": 999}",
+		},
+		{
+			"eth_getBlockByNumber",
+			[]interface{}{
+				"0x1",
+				true,
+			},
+			"{\"jsonrpc\": \"2.0\", \"result\": \"dummy_block\", \"id\": 999}",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.method, func(t *testing.T) {
+			_, _, err := client.SendRPC(tt.method, tt.params)
+			require.NoError(t, err)
+			res, _, err := client.SendRPC(tt.method, tt.params)
+			require.NoError(t, err)
+			RequireEqualJSON(t, []byte(tt.response), res)
+			var count int
+			for _, req := range backend.Requests() {
+				if bytes.Contains(req.Body, []byte(tt.method)) {
+					count++
+				}
+			}
+			require.Equal(t, 1, count)
+			backend.Reset()
+		})
+	}
+}

go/proxyd/integration_tests/failover_test.go

+package integration_tests
+
+import (
+	"fmt"
+	"github.com/ethereum-optimism/optimism/go/proxyd"
+	"github.com/stretchr/testify/require"
+	"net/http"
+	"os"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+const goodResponse = "{\"jsonrpc\": \"2.0\", \"result\": \"hello\", \"id\": 999}"
+const noBackendsResponse = "{\"error\":{\"code\":-32011,\"message\":\"no backends available for method\"},\"id\":999,\"jsonrpc\":\"2.0\"}"
+
+func TestFailover(t *testing.T) {
+	goodBackend := NewMockBackend(SingleResponseHandler(200, goodResponse))
+	defer goodBackend.Close()
+	badBackend := NewMockBackend(nil)
+	defer badBackend.Close()
+
+	require.NoError(t, os.Setenv("GOOD_BACKEND_RPC_URL", goodBackend.URL()))
+	require.NoError(t, os.Setenv("BAD_BACKEND_RPC_URL", badBackend.URL()))
+
+	config := ReadConfig("failover")
+	client := NewProxydClient("http://127.0.0.1:8545")
+	shutdown, err := proxyd.Start(config)
+	require.NoError(t, err)
+	defer shutdown()
+
+	tests := []struct {
+		name    string
+		handler http.Handler
+	}{
+		{
+			"backend responds 200 with non-JSON response",
+			http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(200)
+				w.Write([]byte("this data is not JSON!"))
+			}),
+		},
+		{
+			"backend responds with no body",
+			http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(200)
+			}),
+		},
+	}
+	codes := []int{
+		300,
+		301,
+		302,
+		401,
+		403,
+		429,
+		500,
+		503,
+	}
+	for _, code := range codes {
+		tests = append(tests, struct {
+			name    string
+			handler http.Handler
+		}{
+			fmt.Sprintf("backend %d", code),
+			http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(code)
+			}),
+		})
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			badBackend.SetHandler(tt.handler)
+			res, statusCode, err := client.SendRPC("eth_chainId", nil)
+			require.NoError(t, err)
+			require.Equal(t, 200, statusCode)
+			RequireEqualJSON(t, []byte(goodResponse), res)
+			require.Equal(t, 1, len(badBackend.Requests()))
+			require.Equal(t, 1, len(goodBackend.Requests()))
+			badBackend.Reset()
+			goodBackend.Reset()
+		})
+	}
+
+	t.Run("backend times out", func(t *testing.T) {
+		badBackend.SetHandler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			time.Sleep(2 * time.Second)
+			w.Write([]byte("{}"))
+		}))
+		res, statusCode, err := client.SendRPC("eth_chainId", nil)
+		require.NoError(t, err)
+		require.Equal(t, 200, statusCode)
+		RequireEqualJSON(t, []byte(goodResponse), res)
+		require.Equal(t, 1, len(badBackend.Requests()))
+		require.Equal(t, 1, len(goodBackend.Requests()))
+	})
+
+	t.Run("works with a batch request", func(t *testing.T) {
+		goodBackend.Reset()
+		badBackend.Reset()
+
+		badBackend.SetHandler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.WriteHeader(500)
+		}))
+		res, statusCode, err := client.SendBatchRPC(
+			NewRPCReq("1", "eth_chainId", nil),
+			NewRPCReq("1", "eth_chainId", nil),
+		)
+		require.NoError(t, err)
+		require.Equal(t, 200, statusCode)
+		RequireEqualJSON(t, []byte(asArray(goodResponse, goodResponse)), res)
+		require.Equal(t, 2, len(badBackend.Requests()))
+		require.Equal(t, 2, len(goodBackend.Requests()))
+	})
+}
+
+func TestRetries(t *testing.T) {
+	backend := NewMockBackend(SingleResponseHandler(200, goodResponse))
+	defer backend.Close()
+
+	require.NoError(t, os.Setenv("GOOD_BACKEND_RPC_URL", backend.URL()))
+	config := ReadConfig("retries")
+	client := NewProxydClient("http://127.0.0.1:8545")
+	shutdown, err := proxyd.Start(config)
+	require.NoError(t, err)
+	defer shutdown()
+
+	attempts := int32(0)
+	backend.SetHandler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		incremented := atomic.AddInt32(&attempts, 1)
+		if incremented != 2 {
+			w.WriteHeader(500)
+			return
+		}
+		w.Write([]byte(goodResponse))
+	}))
+
+	// test case where request eventually succeeds
+	res, statusCode, err := client.SendRPC("eth_chainId", nil)
+	require.NoError(t, err)
+	require.Equal(t, 200, statusCode)
+	RequireEqualJSON(t, []byte(goodResponse), res)
+	require.Equal(t, 2, len(backend.Requests()))
+
+	// test case where it does not
+	backend.Reset()
+	attempts = -10
+	res, statusCode, err = client.SendRPC("eth_chainId", nil)
+	require.NoError(t, err)
+	require.Equal(t, 503, statusCode)
+	RequireEqualJSON(t, []byte(noBackendsResponse), res)
+	require.Equal(t, 4, len(backend.Requests()))
+}
+
+func TestOutOfServiceInterval(t *testing.T) {
+	goodBackend := NewMockBackend(SingleResponseHandler(200, goodResponse))
+	defer goodBackend.Close()
+	badBackend := NewMockBackend(SingleResponseHandler(200, goodResponse))
+	defer badBackend.Close()
+
+	require.NoError(t, os.Setenv("GOOD_BACKEND_RPC_URL", goodBackend.URL()))
+	require.NoError(t, os.Setenv("BAD_BACKEND_RPC_URL", badBackend.URL()))
+
+	config := ReadConfig("out_of_service_interval")
+	client := NewProxydClient("http://127.0.0.1:8545")
+	shutdown, err := proxyd.Start(config)
+	require.NoError(t, err)
+	defer shutdown()
+
+	okHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte(goodResponse))
+	})
+	badBackend.SetHandler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(503)
+	}))
+	goodBackend.SetHandler(okHandler)
+
+	res, statusCode, err := client.SendRPC("eth_chainId", nil)
+	require.NoError(t, err)
+	require.Equal(t, 200, statusCode)
+	RequireEqualJSON(t, []byte(goodResponse), res)
+	require.Equal(t, 2, len(badBackend.Requests()))
+	require.Equal(t, 1, len(goodBackend.Requests()))
+
+	res, statusCode, err = client.SendRPC("eth_chainId", nil)
+	require.NoError(t, err)
+	require.Equal(t, 200, statusCode)
+	RequireEqualJSON(t, []byte(goodResponse), res)
+	require.Equal(t, 2, len(badBackend.Requests()))
+	require.Equal(t, 2, len(goodBackend.Requests()))
+
+	res, statusCode, err = client.SendBatchRPC(
+		NewRPCReq("1", "eth_chainId", nil),
+		NewRPCReq("1", "eth_chainId", nil),
+	)
+	require.Equal(t, 2, len(badBackend.Requests()))
+	require.Equal(t, 4, len(goodBackend.Requests()))
+
+	time.Sleep(time.Second)
+	badBackend.SetHandler(okHandler)
+
+	res, statusCode, err = client.SendRPC("eth_chainId", nil)
+	require.NoError(t, err)
+	require.Equal(t, 200, statusCode)
+	RequireEqualJSON(t, []byte(goodResponse), res)
+	require.Equal(t, 3, len(badBackend.Requests()))
+	require.Equal(t, 4, len(goodBackend.Requests()))
+}

go/proxyd/integration_tests/mock_backend_test.go

+package integration_tests
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"github.com/ethereum-optimism/optimism/go/proxyd"
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"sync"
+)
+
+type RecordedRequest struct {
+	Method  string
+	Headers http.Header
+	Body    []byte
+}
+
+type MockBackend struct {
+	handler  http.Handler
+	server   *httptest.Server
+	mtx      sync.RWMutex
+	requests []*RecordedRequest
+}
+
+func SingleResponseHandler(code int, response string) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(code)
+		w.Write([]byte(response))
+	}
+}
+
+func RPCResponseHandler(rpcResponses map[string]string) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		body, err := ioutil.ReadAll(r.Body)
+		if err != nil {
+			panic(err)
+		}
+		req, err := proxyd.ParseRPCReq(body)
+		if err != nil {
+			panic(err)
+		}
+		res := rpcResponses[req.Method]
+		if res == "" {
+			w.WriteHeader(400)
+			return
+		}
+
+		out := &proxyd.RPCRes{
+			JSONRPC: proxyd.JSONRPCVersion,
+			Result:  res,
+			ID:      req.ID,
+		}
+		enc := json.NewEncoder(w)
+		if err := enc.Encode(out); err != nil {
+			panic(err)
+		}
+	}
+}
+
+func NewMockBackend(handler http.Handler) *MockBackend {
+	mb := &MockBackend{
+		handler: handler,
+	}
+	mb.server = httptest.NewServer(http.HandlerFunc(mb.wrappedHandler))
+	return mb
+}
+
+func (m *MockBackend) URL() string {
+	return m.server.URL
+}
+
+func (m *MockBackend) Close() {
+	m.server.Close()
+}
+
+func (m *MockBackend) SetHandler(handler http.Handler) {
+	m.mtx.Lock()
+	m.handler = handler
+	m.mtx.Unlock()
+}
+
+func (m *MockBackend) Reset() {
+	m.mtx.Lock()
+	m.requests = nil
+	m.mtx.Unlock()
+}
+
+func (m *MockBackend) Requests() []*RecordedRequest {
+	m.mtx.RLock()
+	defer m.mtx.RUnlock()
+	out := make([]*RecordedRequest, len(m.requests))
+	for i := 0; i < len(m.requests); i++ {
+		out[i] = m.requests[i]
+	}
+	return out
+}
+
+func (m *MockBackend) wrappedHandler(w http.ResponseWriter, r *http.Request) {
+	m.mtx.Lock()
+	body, err := ioutil.ReadAll(r.Body)
+	if err != nil {
+		panic(err)
+	}
+	clone := r.Clone(context.Background())
+	clone.Body = ioutil.NopCloser(bytes.NewReader(body))
+	m.requests = append(m.requests, &RecordedRequest{
+		Method:  r.Method,
+		Headers: r.Header.Clone(),
+		Body:    body,
+	})
+	m.handler.ServeHTTP(w, clone)
+	m.mtx.Unlock()
+}

go/proxyd/integration_tests/rate_limit_test.go

+package integration_tests
+
+import (
+	"github.com/ethereum-optimism/optimism/go/proxyd"
+	"github.com/stretchr/testify/require"
+	"os"
+	"testing"
+)
+
+type resWithCode struct {
+	code int
+	res  []byte
+}
+
+func TestMaxRPSLimit(t *testing.T) {
+	goodBackend := NewMockBackend(SingleResponseHandler(200, goodResponse))
+	defer goodBackend.Close()
+
+	require.NoError(t, os.Setenv("GOOD_BACKEND_RPC_URL", goodBackend.URL()))
+
+	config := ReadConfig("rate_limit")
+	client := NewProxydClient("http://127.0.0.1:8545")
+	shutdown, err := proxyd.Start(config)
+	require.NoError(t, err)
+	defer shutdown()
+
+	resCh := make(chan *resWithCode)
+	for i := 0; i < 3; i++ {
+		go func() {
+			res, code, err := client.SendRPC("eth_chainId", nil)
+			require.NoError(t, err)
+			resCh <- &resWithCode{
+				code: code,
+				res:  res,
+			}
+		}()
+	}
+
+	codes := make(map[int]int)
+	var limitedRes []byte
+	for i := 0; i < 3; i++ {
+		res := <-resCh
+		code := res.code
+		if codes[code] == 0 {
+			codes[code] = 1
+		} else {
+			codes[code] += 1
+		}
+
+		// 503 because there's only one backend available
+		if code == 503 {
+			limitedRes = res.res
+		}
+	}
+
+	require.Equal(t, 2, codes[200])
+	require.Equal(t, 1, codes[503])
+	RequireEqualJSON(t, []byte(noBackendsResponse), limitedRes)
+}

go/proxyd/integration_tests/testdata/caching.toml

+[server]
+rpc_port = 8545
+
+[backend]
+response_timeout_seconds = 1
+
+[redis]
+url = "$REDIS_URL"
+
+[cache]
+enabled = true
+block_sync_rpc_url = "$GOOD_BACKEND_RPC_URL"
+
+
+[backends]
+[backends.good]
+rpc_url = "$GOOD_BACKEND_RPC_URL"
+ws_url = "$GOOD_BACKEND_RPC_URL"
+
+[backend_groups]
+[backend_groups.main]
+backends = ["good"]
+
+[rpc_method_mappings]
+eth_chainId = "main"
+net_version = "main"
+eth_getBlockByNumber = "main"

go/proxyd/integration_tests/testdata/failover.toml

+[server]
+rpc_port = 8545
+
+[backend]
+response_timeout_seconds = 1
+
+[backends]
+[backends.good]
+rpc_url = "$GOOD_BACKEND_RPC_URL"
+ws_url = "$GOOD_BACKEND_RPC_URL"
+[backends.bad]
+rpc_url = "$BAD_BACKEND_RPC_URL"
+ws_url = "$BAD_BACKEND_RPC_URL"
+
+[backend_groups]
+[backend_groups.main]
+backends = ["bad", "good"]
+
+[rpc_method_mappings]
+eth_chainId = "main"
\ No newline at end of file

go/proxyd/integration_tests/testdata/out_of_service_interval.toml

+[server]
+rpc_port = 8545
+
+[backend]
+response_timeout_seconds = 1
+max_retries = 1
+out_of_service_seconds = 1
+
+[backends]
+[backends.good]
+rpc_url = "$GOOD_BACKEND_RPC_URL"
+ws_url = "$GOOD_BACKEND_RPC_URL"
+[backends.bad]
+rpc_url = "$BAD_BACKEND_RPC_URL"
+ws_url = "$BAD_BACKEND_RPC_URL"
+
+[backend_groups]
+[backend_groups.main]
+backends = ["bad", "good"]
+
+[rpc_method_mappings]
+eth_chainId = "main"
\ No newline at end of file

go/proxyd/integration_tests/testdata/rate_limit.toml

+[server]
+rpc_port = 8545
+
+[backend]
+response_timeout_seconds = 1
+
+[backends]
+[backends.good]
+rpc_url = "$GOOD_BACKEND_RPC_URL"
+ws_url = "$GOOD_BACKEND_RPC_URL"
+max_rps = 2
+
+[backend_groups]
+[backend_groups.main]
+backends = ["good"]
+
+[rpc_method_mappings]
+eth_chainId = "main"
\ No newline at end of file

go/proxyd/integration_tests/testdata/retries.toml

+[server]
+rpc_port = 8545
+
+[backend]
+response_timeout_seconds = 1
+max_retries = 3
+
+[backends]
+[backends.good]
+rpc_url = "$GOOD_BACKEND_RPC_URL"
+ws_url = "$GOOD_BACKEND_RPC_URL"
+
+[backend_groups]
+[backend_groups.main]
+backends = ["good"]
+
+[rpc_method_mappings]
+eth_chainId = "main"
\ No newline at end of file

go/proxyd/integration_tests/testdata/whitelist.toml

+[server]
+rpc_port = 8545
+
+[backend]
+response_timeout_seconds = 1
+
+[backends]
+[backends.good]
+rpc_url = "$GOOD_BACKEND_RPC_URL"
+ws_url = "$GOOD_BACKEND_RPC_URL"
+
+[backend_groups]
+[backend_groups.main]
+backends = ["good"]
+
+[rpc_method_mappings]
+eth_chainId = "main"
\ No newline at end of file

go/proxyd/integration_tests/util_test.go

+package integration_tests
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"github.com/BurntSushi/toml"
+	"github.com/ethereum-optimism/optimism/go/proxyd"
+	"github.com/stretchr/testify/require"
+	"io/ioutil"
+	"net/http"
+	"testing"
+)
+
+type ProxydClient struct {
+	url string
+}
+
+func NewProxydClient(url string) *ProxydClient {
+	return &ProxydClient{url: url}
+}
+
+func (p *ProxydClient) SendRPC(method string, params []interface{}) ([]byte, int, error) {
+	rpcReq := NewRPCReq("999", method, params)
+	body, err := json.Marshal(rpcReq)
+	if err != nil {
+		panic(err)
+	}
+	return p.SendRequest(body)
+}
+
+func (p *ProxydClient) SendBatchRPC(reqs ...*proxyd.RPCReq) ([]byte, int, error) {
+	body, err := json.Marshal(reqs)
+	if err != nil {
+		panic(err)
+	}
+	return p.SendRequest(body)
+}
+
+func (p *ProxydClient) SendRequest(body []byte) ([]byte, int, error) {
+	res, err := http.Post(p.url, "application/json", bytes.NewReader(body))
+	if err != nil {
+		return nil, -1, err
+	}
+	defer res.Body.Close()
+	code := res.StatusCode
+	resBody, err := ioutil.ReadAll(res.Body)
+	if err != nil {
+		panic(err)
+	}
+	return resBody, code, nil
+}
+
+func RequireEqualJSON(t *testing.T, expected []byte, actual []byte) {
+	expJSON := canonicalizeJSON(t, expected)
+	actJSON := canonicalizeJSON(t, actual)
+	require.Equal(t, string(expJSON), string(actJSON))
+}
+
+func canonicalizeJSON(t *testing.T, in []byte) []byte {
+	var any interface{}
+	if in[0] == '[' {
+		any = make([]interface{}, 0)
+	} else {
+		any = make(map[string]interface{})
+	}
+
+	err := json.Unmarshal(in, &any)
+	require.NoError(t, err)
+	out, err := json.Marshal(any)
+	require.NoError(t, err)
+	return out
+}
+
+func ReadConfig(name string) *proxyd.Config {
+	config := new(proxyd.Config)
+	_, err := toml.DecodeFile(fmt.Sprintf("testdata/%s.toml", name), config)
+	if err != nil {
+		panic(err)
+	}
+	return config
+}
+
+func NewRPCReq(id string, method string, params []interface{}) *proxyd.RPCReq {
+	jsonParams, err := json.Marshal(params)
+	if err != nil {
+		panic(err)
+	}
+
+	return &proxyd.RPCReq{
+		JSONRPC: proxyd.JSONRPCVersion,
+		Method:  method,
+		Params:  jsonParams,
+		ID:      []byte(id),
+	}
+}

go/proxyd/integration_tests/validation_test.go

+package integration_tests
+
+import (
+	"github.com/ethereum-optimism/optimism/go/proxyd"
+	"github.com/stretchr/testify/require"
+	"os"
+	"strings"
+	"testing"
+)
+
+const (
+	notWhitelistedResponse        = "{\"jsonrpc\":\"2.0\",\"error\":{\"code\":-32001,\"message\":\"rpc method is not whitelisted\"},\"id\":999}"
+	parseErrResponse              = "{\"jsonrpc\":\"2.0\",\"error\":{\"code\":-32700,\"message\":\"parse error\"},\"id\":null}"
+	invalidJSONRPCVersionResponse = "{\"error\":{\"code\":-32601,\"message\":\"invalid JSON-RPC version\"},\"id\":null,\"jsonrpc\":\"2.0\"}"
+	invalidIDResponse             = "{\"error\":{\"code\":-32601,\"message\":\"invalid ID\"},\"id\":null,\"jsonrpc\":\"2.0\"}"
+	invalidMethodResponse         = "{\"error\":{\"code\":-32601,\"message\":\"no method specified\"},\"id\":null,\"jsonrpc\":\"2.0\"}"
+	invalidBatchLenResponse       = "{\"error\":{\"code\":-32601,\"message\":\"must specify at least one batch call\"},\"id\":null,\"jsonrpc\":\"2.0\"}"
+)
+
+func TestSingleRPCValidation(t *testing.T) {
+	goodBackend := NewMockBackend(SingleResponseHandler(200, goodResponse))
+	defer goodBackend.Close()
+
+	require.NoError(t, os.Setenv("GOOD_BACKEND_RPC_URL", goodBackend.URL()))
+
+	config := ReadConfig("whitelist")
+	client := NewProxydClient("http://127.0.0.1:8545")
+	shutdown, err := proxyd.Start(config)
+	require.NoError(t, err)
+	defer shutdown()
+
+	tests := []struct {
+		name string
+		body string
+		res  string
+		code int
+	}{
+		{
+			"body not JSON",
+			"this ain't an RPC call",
+			parseErrResponse,
+			400,
+		},
+		{
+			"body not RPC",
+			"{\"not\": \"rpc\"}",
+			invalidJSONRPCVersionResponse,
+			400,
+		},
+		{
+			"body missing RPC ID",
+			"{\"jsonrpc\": \"2.0\", \"method\": \"subtract\", \"params\": [42, 23]}",
+			invalidIDResponse,
+			400,
+		},
+		{
+			"body has array ID",
+			"{\"jsonrpc\": \"2.0\", \"method\": \"subtract\", \"params\": [42, 23], \"id\": []}",
+			invalidIDResponse,
+			400,
+		},
+		{
+			"body has object ID",
+			"{\"jsonrpc\": \"2.0\", \"method\": \"subtract\", \"params\": [42, 23], \"id\": {}}",
+			invalidIDResponse,
+			400,
+		},
+		{
+			"bad method",
+			"{\"jsonrpc\": \"2.0\", \"method\": 7, \"params\": [42, 23], \"id\": 1}",
+			parseErrResponse,
+			400,
+		},
+		{
+			"bad JSON-RPC",
+			"{\"jsonrpc\": \"1.0\", \"method\": \"subtract\", \"params\": [42, 23], \"id\": 1}",
+			invalidJSONRPCVersionResponse,
+			400,
+		},
+		{
+			"omitted method",
+			"{\"jsonrpc\": \"2.0\", \"params\": [42, 23], \"id\": 1}",
+			invalidMethodResponse,
+			400,
+		},
+		{
+			"not whitelisted method",
+			"{\"jsonrpc\": \"2.0\", \"method\": \"subtract\", \"params\": [42, 23], \"id\": 999}",
+			notWhitelistedResponse,
+			403,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			res, code, err := client.SendRequest([]byte(tt.body))
+			require.NoError(t, err)
+			RequireEqualJSON(t, []byte(tt.res), res)
+			require.Equal(t, tt.code, code)
+			require.Equal(t, 0, len(goodBackend.Requests()))
+		})
+	}
+}
+
+func TestBatchRPCValidation(t *testing.T) {
+	goodBackend := NewMockBackend(SingleResponseHandler(200, goodResponse))
+	defer goodBackend.Close()
+
+	require.NoError(t, os.Setenv("GOOD_BACKEND_RPC_URL", goodBackend.URL()))
+
+	config := ReadConfig("whitelist")
+	client := NewProxydClient("http://127.0.0.1:8545")
+	shutdown, err := proxyd.Start(config)
+	require.NoError(t, err)
+	defer shutdown()
+
+	tests := []struct {
+		name     string
+		body     string
+		res      string
+		code     int
+		reqCount int
+	}{
+		{
+			"empty batch",
+			"[]",
+			invalidBatchLenResponse,
+			400,
+			0,
+		},
+		{
+			"bad json",
+			"[{,]",
+			parseErrResponse,
+			400,
+			0,
+		},
+		{
+			"not object in batch",
+			"[123]",
+			asArray(parseErrResponse),
+			200,
+			0,
+		},
+		{
+			"body not RPC",
+			"[{\"not\": \"rpc\"}]",
+			asArray(invalidJSONRPCVersionResponse),
+			200,
+			0,
+		},
+		{
+			"body missing RPC ID",
+			"[{\"jsonrpc\": \"2.0\", \"method\": \"subtract\", \"params\": [42, 23]}]",
+			asArray(invalidIDResponse),
+			200,
+			0,
+		},
+		{
+			"body has array ID",
+			"[{\"jsonrpc\": \"2.0\", \"method\": \"subtract\", \"params\": [42, 23], \"id\": []}]",
+			asArray(invalidIDResponse),
+			200,
+			0,
+		},
+		{
+			"body has object ID",
+			"[{\"jsonrpc\": \"2.0\", \"method\": \"subtract\", \"params\": [42, 23], \"id\": {}}]",
+			asArray(invalidIDResponse),
+			200,
+			0,
+		},
+		// this happens because we can't deserialize the method into a non
+		// string value, and it blows up the parsing for the whole request.
+		{
+			"bad method",
+			"[{\"error\":{\"code\":-32600,\"message\":\"invalid request\"},\"id\":null,\"jsonrpc\":\"2.0\"}]",
+			asArray(invalidMethodResponse),
+			200,
+			0,
+		},
+		{
+			"bad JSON-RPC",
+			"[{\"jsonrpc\": \"1.0\", \"method\": \"subtract\", \"params\": [42, 23], \"id\": 1}]",
+			asArray(invalidJSONRPCVersionResponse),
+			200,
+			0,
+		},
+		{
+			"omitted method",
+			"[{\"jsonrpc\": \"2.0\", \"params\": [42, 23], \"id\": 1}]",
+			asArray(invalidMethodResponse),
+			200,
+			0,
+		},
+		{
+			"not whitelisted method",
+			"[{\"jsonrpc\": \"2.0\", \"method\": \"subtract\", \"params\": [42, 23], \"id\": 999}]",
+			asArray(notWhitelistedResponse),
+			200,
+			0,
+		},
+		{
+			"mixed",
+			asArray(
+				"{\"jsonrpc\": \"2.0\", \"method\": \"subtract\", \"params\": [42, 23], \"id\": 999}",
+				"{\"jsonrpc\": \"2.0\", \"method\": \"eth_chainId\", \"params\": [], \"id\": 123}",
+				"123",
+			),
+			asArray(
+				notWhitelistedResponse,
+				goodResponse,
+				parseErrResponse,
+			),
+			200,
+			1,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			res, code, err := client.SendRequest([]byte(tt.body))
+			require.NoError(t, err)
+			RequireEqualJSON(t, []byte(tt.res), res)
+			require.Equal(t, tt.code, code)
+			require.Equal(t, tt.reqCount, len(goodBackend.Requests()))
+		})
+	}
+}
+
+func asArray(in ...string) string {
+	return "[" + strings.Join(in, ",") + "]"
+}

go/proxyd/metrics.go

@@ -149,7 +149,6 @@ var (
 		Buckets:   PayloadSizeBuckets,
 	}, []string{
 		"auth",
-		"method_name",
 	})
 
 	responsePayloadSizesGauge = promauto.NewHistogramVec(prometheus.HistogramOpts{
@@ -161,6 +160,22 @@ var (
 		"auth",
 	})
 
+	cacheHitsTotal = promauto.NewCounterVec(prometheus.CounterOpts{
+		Namespace: MetricsNamespace,
+		Name:      "cache_hits_total",
+		Help:      "Number of cache hits.",
+	}, []string{
+		"method",
+	})
+
+	cacheMissesTotal = promauto.NewCounterVec(prometheus.CounterOpts{
+		Namespace: MetricsNamespace,
+		Name:      "cache_misses_total",
+		Help:      "Number of cache misses.",
+	}, []string{
+		"method",
+	})
+
 	rpcSpecialErrors = []string{
 		"nonce too low",
 		"gas price too high",
@@ -208,10 +223,18 @@ func MaybeRecordSpecialRPCError(ctx context.Context, backendName, method string,
 	}
 }
 
-func RecordRequestPayloadSize(ctx context.Context, method string, payloadSize int) {
-	requestPayloadSizesGauge.WithLabelValues(GetAuthCtx(ctx), method).Observe(float64(payloadSize))
+func RecordRequestPayloadSize(ctx context.Context, payloadSize int) {
+	requestPayloadSizesGauge.WithLabelValues(GetAuthCtx(ctx)).Observe(float64(payloadSize))
 }
 
 func RecordResponsePayloadSize(ctx context.Context, payloadSize int) {
 	responsePayloadSizesGauge.WithLabelValues(GetAuthCtx(ctx)).Observe(float64(payloadSize))
 }
+
+func RecordCacheHit(method string) {
+	cacheHitsTotal.WithLabelValues(method).Inc()
+}
+
+func RecordCacheMiss(method string) {
+	cacheMissesTotal.WithLabelValues(method).Inc()
+}

go/proxyd/proxyd.go

@@ -7,40 +7,47 @@ import (
 	"fmt"
 	"net/http"
 	"os"
-	"os/signal"
-	"syscall"
 	"time"
 
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
-func Start(config *Config) error {
+func Start(config *Config) (func(), error) {
 	if len(config.Backends) == 0 {
-		return errors.New("must define at least one backend")
+		return nil, errors.New("must define at least one backend")
 	}
 	if len(config.BackendGroups) == 0 {
-		return errors.New("must define at least one backend group")
+		return nil, errors.New("must define at least one backend group")
 	}
 	if len(config.RPCMethodMappings) == 0 {
-		return errors.New("must define at least one RPC method mapping")
+		return nil, errors.New("must define at least one RPC method mapping")
 	}
 
 	for authKey := range config.Authentication {
 		if authKey == "none" {
-			return errors.New("cannot use none as an auth key")
+			return nil, errors.New("cannot use none as an auth key")
 		}
 	}
 
+	var redisURL string
+	if config.Redis.URL != "" {
+		rURL, err := ReadFromEnvOrConfig(config.Redis.URL)
+		if err != nil {
+			return nil, err
+		}
+		redisURL = rURL
+	}
+
 	var lim RateLimiter
 	var err error
-	if config.Redis == nil {
+	if redisURL == "" {
 		log.Warn("redis is not configured, using local rate limiter")
 		lim = NewLocalRateLimiter()
 	} else {
-		lim, err = NewRedisRateLimiter(config.Redis.URL)
+		lim, err = NewRedisRateLimiter(redisURL)
 		if err != nil {
-			return err
+			return nil, err
 		}
 	}
 
@@ -51,17 +58,17 @@ func Start(config *Config) error {
 
 		rpcURL, err := ReadFromEnvOrConfig(cfg.RPCURL)
 		if err != nil {
-			return err
+			return nil, err
 		}
 		wsURL, err := ReadFromEnvOrConfig(cfg.WSURL)
 		if err != nil {
-			return err
+			return nil, err
 		}
 		if rpcURL == "" {
-			return fmt.Errorf("must define an RPC URL for backend %s", name)
+			return nil, fmt.Errorf("must define an RPC URL for backend %s", name)
 		}
 		if wsURL == "" {
-			return fmt.Errorf("must define a WS URL for backend %s", name)
+			return nil, fmt.Errorf("must define a WS URL for backend %s", name)
 		}
 
 		if config.BackendOptions.ResponseTimeoutSeconds != 0 {
@@ -86,13 +93,13 @@ func Start(config *Config) error {
 		if cfg.Password != "" {
 			passwordVal, err := ReadFromEnvOrConfig(cfg.Password)
 			if err != nil {
-				return err
+				return nil, err
 			}
 			opts = append(opts, WithBasicAuth(cfg.Username, passwordVal))
 		}
 		tlsConfig, err := configureBackendTLS(cfg)
 		if err != nil {
-			return err
+			return nil, err
 		}
 		if tlsConfig != nil {
 			log.Info("using custom TLS config for backend", "name", name)
@@ -113,7 +120,7 @@ func Start(config *Config) error {
 		backends := make([]*Backend, 0)
 		for _, bName := range bg.Backends {
 			if backendsByName[bName] == nil {
-				return fmt.Errorf("backend %s is not defined", bName)
+				return nil, fmt.Errorf("backend %s is not defined", bName)
 			}
 			backends = append(backends, backendsByName[bName])
 		}
@@ -128,17 +135,17 @@ func Start(config *Config) error {
 	if config.WSBackendGroup != "" {
 		wsBackendGroup = backendGroups[config.WSBackendGroup]
 		if wsBackendGroup == nil {
-			return fmt.Errorf("ws backend group %s does not exist", config.WSBackendGroup)
+			return nil, fmt.Errorf("ws backend group %s does not exist", config.WSBackendGroup)
 		}
 	}
 
 	if wsBackendGroup == nil && config.Server.WSPort != 0 {
-		return fmt.Errorf("a ws port was defined, but no ws group was defined")
+		return nil, fmt.Errorf("a ws port was defined, but no ws group was defined")
 	}
 
 	for _, bg := range config.RPCMethodMappings {
 		if backendGroups[bg] == nil {
-			return fmt.Errorf("undefined backend group %s", bg)
+			return nil, fmt.Errorf("undefined backend group %s", bg)
 		}
 	}
 
@@ -149,34 +156,39 @@ func Start(config *Config) error {
 		for secret, alias := range config.Authentication {
 			resolvedSecret, err := ReadFromEnvOrConfig(secret)
 			if err != nil {
-				return err
+				return nil, err
 			}
 			resolvedAuth[resolvedSecret] = alias
 		}
 	}
 
 	var rpcCache RPCCache
-	if config.Cache != nil && config.Cache.Enabled {
+	var latestHead *LatestBlockHead
+	if config.Cache.Enabled {
+		var getLatestBlockNumFn GetLatestBlockNumFn
+		if config.Cache.BlockSyncRPCURL == "" {
+			return nil, fmt.Errorf("block sync node required for caching")
+		}
+		blockSyncRPCURL, err := ReadFromEnvOrConfig(config.Cache.BlockSyncRPCURL)
+		if err != nil {
+			return nil, err
+		}
+
 		var cache Cache
-		if config.Redis != nil {
-			if cache, err = newRedisCache(config.Redis.URL); err != nil {
-				return err
+		if redisURL != "" {
+			if cache, err = newRedisCache(redisURL); err != nil {
+				return nil, err
 			}
 		} else {
 			log.Warn("redis is not configured, using in-memory cache")
 			cache = newMemoryCache()
 		}
 
-		var getLatestBlockNumFn GetLatestBlockNumFn
-		if config.Cache.BlockSyncRPCURL == "" {
-			return fmt.Errorf("block sync node required for caching")
-		}
-		latestHead, err := newLatestBlockHead(config.Cache.BlockSyncRPCURL)
+		latestHead, err = newLatestBlockHead(blockSyncRPCURL)
 		if err != nil {
-			return err
+			return nil, err
 		}
 		latestHead.Start()
-		defer latestHead.Stop()
 
 		getLatestBlockNumFn = func(ctx context.Context) (uint64, error) {
 			return latestHead.GetBlockNum(), nil
@@ -194,12 +206,17 @@ func Start(config *Config) error {
 		rpcCache,
 	)
 
-	if config.Metrics != nil && config.Metrics.Enabled {
+	if config.Metrics.Enabled {
 		addr := fmt.Sprintf("%s:%d", config.Metrics.Host, config.Metrics.Port)
 		log.Info("starting metrics server", "addr", addr)
 		go http.ListenAndServe(addr, promhttp.Handler())
 	}
 
+	// To allow integration tests to cleanly come up, wait
+	// 10ms to give the below goroutines enough time to
+	// encounter an error creating their servers
+	errTimer := time.NewTimer(10 * time.Millisecond)
+
 	if config.Server.RPCPort != 0 {
 		go func() {
 			if err := srv.RPCListenAndServe(config.Server.RPCHost, config.Server.RPCPort); err != nil {
@@ -224,15 +241,20 @@ func Start(config *Config) error {
 		}()
 	}
 
-	sig := make(chan os.Signal, 1)
-	signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
-	recvSig := <-sig
-	log.Info("caught signal, shutting down", "signal", recvSig)
+	<-errTimer.C
+	log.Info("started proxyd")
+
+	return func() {
+		log.Info("shutting down proxyd")
+		if latestHead != nil {
+			latestHead.Stop()
+		}
 		srv.Shutdown()
 		if err := lim.FlushBackendWSConns(backendNames); err != nil {
 			log.Error("error flushing backend ws conns", "err", err)
 		}
-	return nil
+		log.Info("goodbye")
+	}, nil
 }
 
 func secondsToDuration(seconds int) time.Duration {

go/proxyd/rpc.go

@@ -46,30 +46,22 @@ func IsValidID(id json.RawMessage) bool {
 	return len(id) > 0 && id[0] != '{' && id[0] != '['
 }
 
-func ParseRPCReq(r io.Reader) (*RPCReq, error) {
-	body, err := ioutil.ReadAll(r)
-	if err != nil {
-		return nil, wrapErr(err, "error reading request body")
-	}
-
+func ParseRPCReq(body []byte) (*RPCReq, error) {
 	req := new(RPCReq)
 	if err := json.Unmarshal(body, req); err != nil {
 		return nil, ErrParseErr
 	}
 
-	if req.JSONRPC != JSONRPCVersion {
-		return nil, ErrInvalidRequest("invalid JSON-RPC version")
-	}
-
-	if req.Method == "" {
-		return nil, ErrInvalidRequest("no method specified")
-	}
+	return req, nil
+}
 
-	if !IsValidID(req.ID) {
-		return nil, ErrInvalidRequest("invalid ID")
+func ParseBatchRPCReq(body []byte) ([]json.RawMessage, error) {
+	batch := make([]json.RawMessage, 0)
+	if err := json.Unmarshal(body, &batch); err != nil {
+		return nil, err
 	}
 
-	return req, nil
+	return batch, nil
 }
 
 func ParseRPCRes(r io.Reader) (*RPCRes, error) {
@@ -86,6 +78,22 @@ func ParseRPCRes(r io.Reader) (*RPCRes, error) {
 	return res, nil
 }
 
+func ValidateRPCReq(req *RPCReq) error {
+	if req.JSONRPC != JSONRPCVersion {
+		return ErrInvalidRequest("invalid JSON-RPC version")
+	}
+
+	if req.Method == "" {
+		return ErrInvalidRequest("no method specified")
+	}
+
+	if !IsValidID(req.ID) {
+		return ErrInvalidRequest("invalid ID")
+	}
+
+	return nil
+}
+
 func NewRPCErrorRes(id json.RawMessage, err error) *RPCRes {
 	var rpcErr *RPCErr
 	if rr, ok := err.(*RPCErr); ok {

go/proxyd/server.go

@@ -6,6 +6,8 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"io/ioutil"
+	"math"
 	"net/http"
 	"strconv"
 	"strings"
@@ -22,6 +24,7 @@ const (
 	ContextKeyAuth          = "authorization"
 	ContextKeyReqID         = "req_id"
 	ContextKeyXForwardedFor = "x_forwarded_for"
+	MaxBatchRPCCalls        = 25
 )
 
 type Server struct {
@@ -49,6 +52,11 @@ func NewServer(
 	if cache == nil {
 		cache = &NoopRPCCache{}
 	}
+
+	if maxBodySize == 0 {
+		maxBodySize = math.MaxInt64
+	}
+
 	return &Server{
 		backendGroups:      backendGroups,
 		wsBackendGroup:     wsBackendGroup,
@@ -122,15 +130,66 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 		"user_agent", r.Header.Get("user-agent"),
 	)
 
-	bodyReader := &recordLenReader{Reader: io.LimitReader(r.Body, s.maxBodySize)}
-	req, err := ParseRPCReq(bodyReader)
+	body, err := ioutil.ReadAll(io.LimitReader(r.Body, s.maxBodySize))
+	if err != nil {
+		log.Error("error reading request body", "err", err)
+		writeRPCError(ctx, w, nil, ErrInternal)
+		return
+	}
+	RecordRequestPayloadSize(ctx, len(body))
+
+	if body[0] == '[' {
+		reqs, err := ParseBatchRPCReq(body)
 		if err != nil {
-		log.Info("rejected request with bad rpc request", "source", "rpc", "err", err)
+			log.Error("error parsing batch RPC request", "err", err)
 			RecordRPCError(ctx, BackendProxyd, MethodUnknown, err)
+			writeRPCError(ctx, w, nil, ErrParseErr)
+			return
+		}
+
+		if len(reqs) > MaxBatchRPCCalls {
+			RecordRPCError(ctx, BackendProxyd, MethodUnknown, ErrTooManyBatchRequests)
+			writeRPCError(ctx, w, nil, ErrTooManyBatchRequests)
+			return
+		}
+
+		if len(reqs) == 0 {
+			writeRPCError(ctx, w, nil, ErrInvalidRequest("must specify at least one batch call"))
+			return
+		}
+
+		batchRes := make([]*RPCRes, len(reqs), len(reqs))
+		for i := 0; i < len(reqs); i++ {
+			req, err := ParseRPCReq(reqs[i])
+			if err != nil {
+				log.Info("error parsing RPC call", "source", "rpc", "err", err)
+				batchRes[i] = NewRPCErrorRes(nil, err)
+				continue
+			}
+
+			batchRes[i] = s.handleSingleRPC(ctx, req)
+		}
+
+		writeBatchRPCRes(ctx, w, batchRes)
+		return
+	}
+
+	req, err := ParseRPCReq(body)
+	if err != nil {
+		log.Info("error parsing RPC call", "source", "rpc", "err", err)
 		writeRPCError(ctx, w, nil, err)
 		return
 	}
-	RecordRequestPayloadSize(ctx, req.Method, bodyReader.Len)
+
+	backendRes := s.handleSingleRPC(ctx, req)
+	writeRPCRes(ctx, w, backendRes)
+}
+
+func (s *Server) handleSingleRPC(ctx context.Context, req *RPCReq) *RPCRes {
+	if err := ValidateRPCReq(req); err != nil {
+		RecordRPCError(ctx, BackendProxyd, MethodUnknown, err)
+		return NewRPCErrorRes(nil, err)
+	}
 
 	group := s.rpcMethodMappings[req.Method]
 	if group == "" {
@@ -143,16 +202,11 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 			"method", req.Method,
 		)
 		RecordRPCError(ctx, BackendProxyd, MethodUnknown, ErrMethodNotWhitelisted)
-		writeRPCError(ctx, w, req.ID, ErrMethodNotWhitelisted)
-		return
+		return NewRPCErrorRes(req.ID, ErrMethodNotWhitelisted)
 	}
 
 	var backendRes *RPCRes
-	backendRes, err = s.cache.GetRPC(ctx, req)
-	if err == nil && backendRes != nil {
-		writeRPCRes(ctx, w, backendRes)
-		return
-	}
+	backendRes, err := s.cache.GetRPC(ctx, req)
 	if err != nil {
 		log.Warn(
 			"cache lookup error",
@@ -160,6 +214,9 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 			"err", err,
 		)
 	}
+	if backendRes != nil {
+		return backendRes
+	}
 
 	backendRes, err = s.backendGroups[group].Forward(ctx, req)
 	if err != nil {
@@ -169,8 +226,7 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 			"req_id", GetReqID(ctx),
 			"err", err,
 		)
-		writeRPCError(ctx, w, req.ID, err)
-		return
+		return NewRPCErrorRes(req.ID, err)
 	}
 
 	if backendRes.Error == nil {
@@ -183,7 +239,7 @@ func (s *Server) HandleRPC(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	writeRPCRes(ctx, w, backendRes)
+	return backendRes
 }
 
 func (s *Server) HandleWS(w http.ResponseWriter, r *http.Request) {
@@ -294,6 +350,18 @@ func writeRPCRes(ctx context.Context, w http.ResponseWriter, res *RPCRes) {
 	RecordResponsePayloadSize(ctx, ww.Len)
 }
 
+func writeBatchRPCRes(ctx context.Context, w http.ResponseWriter, res []*RPCRes) {
+	w.WriteHeader(200)
+	ww := &recordLenWriter{Writer: w}
+	enc := json.NewEncoder(ww)
+	if err := enc.Encode(res); err != nil {
+		log.Error("error writing batch rpc response", "err", err)
+		RecordRPCError(ctx, BackendProxyd, MethodUnknown, err)
+		return
+	}
+	RecordResponsePayloadSize(ctx, ww.Len)
+}
+
 func instrumentedHdlr(h http.Handler) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		respTimer := prometheus.NewTimer(httpRequestDurationSumm)